The present invention sets forth an article provided with a non-stick coating whose adhesion to the aforesaid article and durability are improved, a manufacturing process for such an article, and a composition suitable to improve the adhesion of a non-stick coating to an article.
The non-stick coatings used to produce cookware to which food does not stick during cooking are usually based on fluorocarbon polymers, such as for example, polytetrafluoroethylene (PTFE), FEP, and the like, or on silicones.
When the article to be coated is a metallic substrate, such as aluminum or cast iron, gritblasting with an abrasive is usually recommended to insure adhesion of the coating to the substrate.
When the substrate is glass or glass ceramic, gritblasting is not suitable, in particular for a PTFE coating. Because of the porosity of the coating, the polymer/substrate interface is, in use, rapidly exposed to water detergents and grease, so that the adhesion of the coating to the substrate, which is mainly a kind of anchoring, is not sufficient to avoid staining or delamination on the aforesaid interface. The damage is particularly visible when the substrate is a transparent glass, such as Pyrex.sup.R brand cookware.
In order to improve adhesion of the non-stick coating to the substrate of the article to be coated, it was proposed in the U.S. Pat. No. 3,558,345, to use aminoalkyltrialkoxysilanes as coupling agents applied on the substrate before application of the non-stick coating. Typically the glass substrate is dipped into a diluted solution of the silane coupling agent for sufficient time, approximately 5 min. to 4 hrs., so as to have hydrolysis of the alkoxy groups, then condensation of the resulting --OH groups with the silanol (.dbd.SiOH) groups existing at the glass surface (see E.P. PLUEDDEMAN, Silylated surfaces, edited by D.E. Leyden and W. Collins, Gordon and Breach Science Publishers, N.Y., 31, 1978). Besides, the aminoalkyl groups have a high (bonding) interaction with the organic coating. Nevertheless for the condensation reaction to develop sufficiently, it is necessary for the substrate surface to be exempt from grease or other organic pollutants. Consequently the surface to be coated has to be thoroughly cleaned with a detergent or an organic solvent, such as alcohol, acetone and the like, then dried, to insure that silanol groups are present on the aforesaid surface, which process is, on an industrial scale, a serious inconvenience. Moreover this process is valid only for glass substrates.